The Department of Health said having been alerted to the plans on Tuesday about the conference it immediately asked each of the trusts and all the other health organisations to explain the necessity to attend and how much it was to cost.

A spokesman added: “The department’s permanent secretary Richard Pengelly wrote to Trusts and other HSC organisations in September 2016, reminding them of the need for effective and proportionate controls on staff travel.

“In particular, it was emphasised that all travel must: be fully justified in terms of making an important contribution to the business needs of the organisation; represent value for money; and not give grounds for public criticism.

“Having been alerted yesterday to plans for the Amsterdam conference, the department immediately wrote to Trusts and other HSC bodies. They were asked for full details of staff numbers attending and the costs involved; and to urgently explain how the planned travel complied with the criteria set out in September 2016.”

Former public sector union representative Bumper Graham said that while the conference would no doubt be worthwhile, staff representation had to be proportionate.

He described the number of staff going from the Belfast Trust as "exceptionally high".

"In situations like this a small number should attend," he said.

"There is no reason whatsoever for the Belfast Trust to be sending 61."